1. Technical Field of the Invention
The present invention relates in general to oil field testing and production equipment and in particular to the process of measuring polished rod loads and polished rod acceleration associated with a well pumping unit and recording the measured data onto a nonvolatile storage medium. The measurements are made and recorded by an apparatus attached to the polished rod thus eliminating the use of cables that would otherwise extend from a stationary apparatus to the polished rod.
2. Description of the Related Art
A number of solutions have been proposed in the prior art for measurement of stroke length of well pumping units.
One device for making measurements of the vertical positions of polished rods is made by Delta-X Corporation of Houston, Tex. This equipment is referred to as an AT-01 Angle Transducer.TM.. It is mounted to the Sampson Post of a pumping unit. A potentiometer shaft from an angle transducer is connected by means of mechanical linkages to a clamp mounted on the pumping unit beam. The device thus measures the angle between the Sampson Post and the pumping unit beam. By knowing specific pumping unit dimensions and applying simple geometrical formulae, the stroke length and stroke position of the pumping unit can then be inferred. However, the device requires precise alignment between the structural members of the pumping unit. With continuous operation and vibrations resulting from the oscillating pumping unit, misalignment and wear of the potentiometer mechanism eventually occurs to cause the position determination to become inaccurate.
Another use of a similar device for measurement of vertical position on a beam pumping unit is manufactured by NABLA Corporation of Midland, Tex. This position indicating device is somewhat similar to that of Delta-X except that the potentiometer is mounted above the carrier bar and is activated by a taut line that is attached to a fixed reference point, generally the wellhead. This mechanical windlass device requires accurate alignment for determination of the vertical position of the polished rod as it strokes up and down during a pumping cycle. Wind induced forces acting on the extended taut line can cause it to become bowed, resulting in inaccurate measurements of stroke length. Neither of these known methods directly measure the vertical or lateral acceleration of the moving polished rod.
The loads on a polished rod can be measured by use of a load cell that uses strain gauges. One such use of a strain gauge load cell for making polished rod load measurements is reference in U.S. Pat. No. 4,090,405 to McKee. This disclosure shows a segmented device that is clamped to the polished rod and has surfaces above and below the position of a cemented strain gauge for transferring load to the device. The transferred load stresses the stain gauge. U.S. Pat. No. 3,355,938 to Neely et al references a load cell that includes a jack screw mechanism for transferring load to the cell that includes strain gauge. A still further device is a load cell manufactured by Interface, Inc. of Scottsdale, Ariz. This is referred to as a LoadTrol.TM. load cell. This device is installed on the polished rod above the hanger carrier bar and below the polished rod clamp. When the load cell is subjected to compressional loads, the resistance through the strain gauge network, although very small, is measured and the strain so calculated is indicative of the loads at the polished rod. All of these devices require an electrical cable to transfer measured data from the strain gauges and polished rod position indicator to a storage medium for analysis. The cable and the end connectors introduce additional resistance to that which comes by virtue of the strain imposed on the load cell along, thus causing inaccuracies in the actual loads being applied at the polished rod. In addition, improper identification of the load cell may result in incorrect calibration reference.
Therefore, there is a need for a device that can provide accurate real time measurement and recording of the vertical and lateral motion of the polished rod and polished rod load information without the necessity of a long electrical cable used by the prior art for transfer of the measurements to a storage medium.
It is an object of this invention to provide a device for real time measurement of vertical and lateral acceleration, velocity, linear position and stroking frequency of a polished rod during pumping operations.
It is a further object of this invention to provide a device for use on a well pumping unit located at the earth's surface that can measure, in real time, loads and positional information on the pumping unit polished rod so that such loads and position information can be synchronized to allow determination of loads and position at the subsurface fluid pump located at the bottom of the well.
It is a further object of this invention to provide a device for use on a well pumping unit to provide polished rod load and positional information that does not have moving parts and is therefore not susceptible to mechanical wear.
It is a further object of this invention to provide an electronic recording device for use on a well pumping unit, the recording device having built-in intelligence to identify the load cell being read for proper calibration reference and to record real time polished rod data onto a non-volatile data card without the necessity of a long electrical cable generally associated with data transfer to external storage devices.
It is still a further object of this invention to provide an intelligent polished rod mounted device that when integrated with a communication radio can provide telemetered real time measured events at the surface, such as acceleration and polished rod load. Such information can be telemetered to a central location for analysis of the pumping system.